Tecumseh HH120 Won't Start

Hello all.

I've got a 1968 Tecumseh HH120 in a good old SS 12. The fellow I bought it from said it ran. but needed a head gasket. So I purchased and installed a new gasket, and also cleaned the carburetor, and bought a new spark plug.

Now it cranks fine, but refuses to start. It's got spark, 100psi of compression, and gas comes out the carburetor. Timing appears fine. I did spray carburetor cleaner, and later on, a little gas, into the cylinder, and it didn't even backfire.

This one's really got me stumped. Any help would be greatly appreciated! I can answer questions.
Thanks!

Gas coming OUT of the carb?

Clean and dry the spark plug, and make a few restart attempts. Pull the plug again. Is it wet, or dry?

If wet, could be flooding horribly. Check fuel inlet valve/float.

Timing APPEARS fine, or have you verified it? Amongst other things, check the flywheel (timing) key. If at any point the flywheel nut was not torqued to spec, the key may have sheared. If this happens, the spark timing goes out, and it won't run right if at all.

When you had it all apart, did you disturb the camshaft, tappets, or any other part of the valvetrain? Throwing the valve timing out will cause a no-fire.

Not exactly coming out the carb, per say, but if you hold your hand over the outlet, it will get wet.
The spark plug is definitely not flooded, but it's not completely dry.

How do I check timing, exactly? This is a solid state ignition model.

And I never had the crankcase open. Just the head off.

To check ignition timing, inspect the aforementioned timing key. Remember to properly re-torque the flywheel nut when you're done, or you'll shear it for sure.

To check valve timing, you'll have to open it up and check the timing marks on the timing gears.

Observe the valves, and see if they are both cycling and sealing correctly.

Are you using fresh fuel? Are you 100% sure you have spark?

If the spark timing is okay, it sounds like you have a valve timing issue, especially if gas is blowing backwards out of the carb. Here is a really dumb question, is the engine spinning the right way when trying to start, and not backwards?

Ok, I don't think I'll be able to check timing, that flywheels on there good.
Valve timing shouldn't be a problem, as the motor has never been opened. It's got plenty of compression, so the valves should be sealing fine.

The fuel is about 2 weeks old, and I am certain there is spark.

Yes Stretch, the motor is going the right way. As I said before, it's not blowing out the carb, persay, but if I put my hand over the intake, your hand will get damp.

If you remove the flywheel nut and any washers under it, you may well be able to eyeball the key without actually removing the 'wheel.

Try removing the spark plug, and pouring a teaspoon of fresh fuel directly into the combustion chamber. Reinstall the spark plug, and crank it over. Report results.

Alright, I'll check the key if the gas fails.
I did put a little bit (not quite a teaspoon) in there, and nothing happened. As well as some (highly flammable) carburetor cleaner.

Well- if gas or carb cleaner doesn't pop, you're down to spark, timing, or compression. You say you've got spark, but never assume anything. Sometimes a plug that will fire under atmospheric conditions will not fire under compression. It's worth your while to try another plug. You say you have 100psi compression, and I can only assume you used a compression tester in order to determine that. So- spark and timing.

Yeah, it's got lots of white spark. I'm not in a good situation to go buy a new plug at the moment. I may be able to pull one out of my snowmobile, I think they might be the same. I did buy the current spark plug three days ago.

And yes, I had a compression tester.

Would you be able to explain how ignition timing works with solid state ignition? There's no magnets, just four flat spots on the flywheel.

Also, I may have found a clue. The guy I bought it from, said it would occasionally cut out. He said he sanded the flat spot on the flywheel, and replaced the spark plug wire. I can tell, the plug wire is obviously original. Don't know if that helps at all.

Thanks for all the help!

This was the ad for the tractor. The guy never took it down.

http://nh.craigslist.org/grd/3965799942.html

Did you buy the plug brand new? If so sometimes they don't work even brand new you may have just gotten a bad plug

Yeah, it is brand new. I can see the spark when I crank it tho. If it stops raining, I'll see if I can find another plug!

Ya I would try that first see if you can find another plug then go from there

Given the age of the engine (now that I think about it)- what sort of shape are the breaker points and condenser in?

What year is the engine?

Yes, I was told it's a 1968.

Doc, it's a Solid State ignition module. No points, no condenser, no magnets.

I tried putting fuel in the cylinder, (this is the weird part), and after cranking for 10 seconds with no attempt at starting, I checked the plug again. Completely dry. Now that I think of it, I have never seen the plug wet. Yet, I have tried gas and starting fluid in the cylinder. The gas is that close, but it won't stick to the plug. Why?

Does the oil smell like gas?

Not that I've noticed. Never taken a whiff down the dipstick tho.

It has plenty of compression tho, if the gas was getting past the rings that bad, I would think it'd have no compression.

Do you notice gas around the exhaust? Maybe you have a valve stuck open. What I would do it pull the head and make sure both valves open and close completely

Yah, the valves are definitely not stuck open. Compression again. And when I bought it, the head was off. So I got a good look in there.

well, if it has good spark, good fuel and good compression it can really be very few things - first on my mind is timing. Spark may be hitting at wrong time, or the valves may not be opening at the right intervals. Best suggestion I can give at this point. Still, that old of an engine theres not much that can go wrong.

Well my latest breakthrough suggests the plug is not getting wet. Even after I dump gas in the cylinder...

BlackMountian88 wrote:

Well my latest breakthrough suggests the plug is not getting wet. Even after I dump gas in the cylinder...

then it has to be leaking past the rings somehow.